Curable organopolysiloxane compositions are used for sealing and/or bonding optical semiconductor elements in optical semiconductor devices having optical semiconductor elements such as photocouplers, light-emitting diodes, solid-state image pickup elements, or the like. It is required that cured bodies of such compositions neither absorb nor scatter the light emitted or received from semiconductor elements. Furthermore, in order to improve reliability of the optical semiconductor devices, it is desired that the cured bodies could not discolor or decrease in the bonding strength.
Japanese Unexamined Patent Application Publication (hereinafter referred to as “Kokai”) 2006-342200 discloses a curable organopolysiloxane composition that can form a cured body having high hardness and high light transmittance. However, the cured body produced from such a composition can be either easily damaged during manufacture or use of an optical semiconductor device, or can easily delaminate from the optical semiconductor element or a package of such element.
Furthermore, Kokai 2007-63538 and Kokai 2008-120843 disclose curable organopolysiloxane compositions that can form cured bodies having excellent impact-resistant properties. However, since with the lapse of time such cured bodies are subject to yellowing, they are not suitable for sealing or bonding optical semiconductor elements of optical semiconductor devices that are intended for long-time use at high temperatures.
It is an object of the present invention to provide a curable organopolysiloxane composition that can form a cured body having long-lasting properties of light transmittance and bondability, and having relatively low hardness. It is another object to provide an optical semiconductor device that possesses excellent reliability.